Compass/Transcript
Transcript Old Version Update Text reads: The Mysteries of Life with Tim and Moby Tim and Moby are on a sailboat. Moby is steering the boat and manning the sails. He pulls on the sail, which nearly hits Tim in the head. Tim ducks frantically. TIM: Ahh! MOBY: Beep. TIM: You have to tell me to duck before you do that. Tim reads from a typed letter. TIM: Dear Tim & Moby, how does a compass work? From, Henry. Compasses are pretty cool. Pretty much wherever you are on Earth, a compass points north. Tim holds out a compass and moves it back and forth. As the compass changes position, its needle adjusts so that it is always pointing in the same direction. TIM: Compasses can help you navigate. Sailors rely on them all the time. An animation shows a boat moving on a map marked with the directions around the edges. Going clockwise from the top: N is for North, E is for East, S is for South, and W is for West. The boat moves across the map from the southeast corner to the northwest, following a dotted line. TIM: Once you know what direction north is, all the other directions fall into place. Right now, we need to be going northwest. Tim leans over the edge of the boat and holds out his compass. TIM: I think we’re a little off course. MOBY: Beep. Moby adjusts the sail. TIM: A compass is a really simple tool. It has a small needle made of iron or steel. The needle is actually a magnet with a north pole and a south pole. And it's balanced on a smooth pivot so that it can swing around freely. An animation shows a compass, with the north and south poles labeled. The needle moves around as Tim describes. TIM: Wherever the north pole is pointing, that's north. MOBY: Beep. TIM: It works because Earth is really a giant magnet! It produces a magnetic field, an invisible area of force that extends all around it. An image shows the Earth as seen from space. A bar magnet appears right down the center, extending roughly from the Earth's north pole to its south pole. Rings ripple out from either side of the earth, curving inward at the top and bottom of the Earth’s sphere to represent the invisible magnetic field. TIM: That field makes a compass's needle swing into a north-south position. Next to the image of the Earth with a magnet appears an almost identical image, but the magnet has been replaced by a compass's needle. MOBY: Beep. TIM: Hey, good question! With magnets, opposite poles attract and like poles repel each other. Side-by-side animations show Moby holding a magnet in each of his hands. In one animation, the north pole of one magnet faces the south pole of the other, and Moby easily connects them. In the other animation, the north poles of both magnets face each other and Moby cannot get them to touch. TIM: So how come the north pole of the compass's needle points north? As it turns out, Earth's magnetic pole is flipped: Magnetic south is in the geographic north, and vice-versa. The image of the Earth with the bar magnet down the middle reappears, and the ends of the magnet are labeled. The end of the magnet closest to Earth's geographic north is labeled with an S, and the end that is closest to the geographic south is labeled with an N. MOBY: Beep. Moby looks confused. TIM: It's not as crazy as it sounds. The compass is a very old invention. It was developed before people had any idea how it really worked. They just knew that one end of the magnetized needle would always point north. An animation shows a Chinese explorer on a boat, holding what looks like a compass needle tied to a string. The needle sways to point north. TIM: So naturally, people began referring to the opposite ends of all magnets as north and south. A clock swipes across the animation to indicate the passage of time. A new animation shows a European ship captain steering a boat and holding a circular compass with all the directions labeled around the edges. TIM: Really though, they could have called it anything: A and B, plus and minus, whatever. MOBY: Beep. TIM: Oh, yeah, that's another little wrinkle. The magnetic poles are slightly offset from the geographic poles. The image of the Earth with the bar magnet down the middle reappears. A second, smaller magnet pops up at the magnetic south. Then, a striped pole pops up at the geographic north pole, which is to the northeast of the magnetic south. A dotted line extends out from the geographic north pole marker, showing the tilt of Earth's rotational axis. TIM: The closer you get to the poles, the more this difference matters. If you're really far north, a compass may actually point you east, west, or even south! An animation shows Santa Claus in his sled. He is close to the geographic north pole marker, and he is staring at a compass with confusion. He holds the compass directly towards the marker and the needle points due east. TIM: But the rest of us can still use a compass to get where we're going. We just have to account for the magnetic variation. That's the difference between magnetic north and True, or geographic, North. An animation shows the north pole as seen from space, a magnet stands in for the magnetic pole, while a striped pole indicates True North. TIM: Let's see, from here, the variation is about 5 degrees west. Two dotted lines move from a point on Earth. One travels to the magnet while the other travels to the striped pole. An arrow moves from one dotted line to the other. The arc formed by the arrow is labeled 5 degrees. TIM: In other words, the needle is pointing 5 degrees west of True North. So we just need to adjust our compass 5 degrees to the east. And then adjust our navigation until we're pointing the right way. Tim holds out his compass over the map. White arrows extend out from the compass, point straight towards the direction labels on the map. A second set of black arrows appears beside the white ones, rotated 5 degrees west to account for the magnetic variation. Tim adjusts the compass as described. MOBY: Beep. Moby leans over the edge of the boat, extending an arm outward in imitation of a compass. TIM: You're too heavy and you're not magnetic. MOBY: Beep. TIM: You are magnetic? MOBY: Beep. Moby closes his eyes and emits an electric hum. The anchor comes flying out of the water and knocks Moby off the boat. MOBY: Beep. TIM: Uhh… duck. Category:BrainPOP Transcripts